Process for producing tubular ring with beads and die for use therein

ABSTRACT

A metal mold is disposed adjacent to the outer circumference of a base ring, and has a molding face in the inner circumference and a plurality of grooves for forming beads on the molding face along the circumferential direction. A coil for electromagnetic forming is disposed adjacent to the inner circumference of the base ring. When a momentary large current is applied to the coil in this arrangement, the diameter of the base ring is expanded by pressing the base ring toward the molding face of the metal mold such that the base ring is molded into a shape corresponding to the molding face by electromagnetic forming. Improvements such as a metal mold capable of degassing, a separable metal mold, roll-correcting after electromagnetic forming, application of momentary large current over several times, a metal mold with a cutting blade, use of a base ring with a large number of holes, and a metal mold with positioning means are then added. With these improvements, a highly accurate cylindrical ring with beads can be produced at low cost and with high productivity.

TECHNICAL FIELD

The present invention relates to methods for manufacturing cylindricalrings with beads available to, for example, reinforced rings forrun-flat tires, and relates to metal molds used for the methods.

BACKGROUND ART

Electromagnetic forming is a method in which a momentary large currentis applied to a coil to generate a strong magnetic field such that anobject (conductor) disposed in the magnetic field is molded by aninteraction between an eddy current generated at the object and themagnetic field. The electromagnetic forming is a known techniquedisclosed in, for example, Japanese Unexamined Patent ApplicationPublication Nos. 6-312226, 9-166111, 58-4601, and the like. Themomentary large current is a current with a value of, for example, 10 kAor more.

Japanese Unexamined Patent Application Publication No. 6-312226discloses an application of this electromagnetic forming to processingof a cylindrical member (hollow workpiece). According to thedescription, a coil for electromagnetic forming is inserted in thehollow workpiece of an extruded aluminum material, and molds for formingan expanded-tube shape are disposed adjacent to the outer circumferenceof the hollow workpiece E having a length corresponding to the coil. Byapplying a momentary large current to the coil in this arrangement, theouter circumference of the hollow workpiece is pressed toward the molds,and thus the outer circumference is molded into a shape corresponding tothe molds. In this manner, a hollow component of which the cross-sectionis changed in the longitudinal direction is produced.

However, when the above-described method was simply applied formanufacture of a cylindrical ring with beads, a dimensional accuracy ofproducts was insufficient, and the productivity could not be increasedeither. In order to put the method for manufacturing the cylindricalring with the beads by electromagnetic forming to practical use, variousadditional schemes have been required.

The present invention is produced so as to solve the problems of theknown method for manufacturing the cylindrical ring with the beads. Itis an object of the present invention to produce highly accuratecylindrical rings with beads at low cost and with high productivity.

DISCLOSURE OF INVENTION

Methods for manufacturing a cylindrical ring with beads according to thepresent invention are based on the steps of disposing a metal moldadjacent to the outer circumference or the inner circumference of aclosed metallic base ring, the metal mold having a molding face thatfaces the base ring and having grooves for forming the beads on themolding face along the circumferential direction; disposing a coil forelectromagnetic forming at the opposite side of the metal mold such thatthe base ring is interposed therebetween; applying a momentary largecurrent to the coil in this arrangement; and deforming the base ring bypressing the base ring toward the molding face of the metal mold suchthat the base ring is molded into a shape corresponding to the moldingface by electromagnetic forming, and improvements are added on these.

First, manufacture of the cylindrical ring with the beads byelectromagnetic forming will now be described, the present inventiondepending on the manufacture.

In the present invention, the beads mean ribs protruding in thedirection of the external diameter of the cylindrical ring. Thecylindrical ring with the beads according to the present inventionincludes, for example, a reinforced ring for a run-flat tire.

The above-described basic methods include the following two variations:That is to say, a method including the steps of disposing a metal moldadjacent to the outer circumference of a closed metallic base ring, themetal mold having a molding face in the inner circumference and havinggrooves for forming the beads on the molding face along thecircumferential direction; disposing a coil for electromagnetic formingadjacent to the inner circumference of the base ring; applying amomentary large current to the coil in this arrangement; and expandingthe diameter of the base ring by pressing the base ring toward themolding face of the metal mold such that the base ring is molded into ashape corresponding to the molding face by electromagnetic forming(so-called flaring processing), and a method including the steps ofdisposing a metal mold adjacent to the inner circumference of a closedmetallic base ring, the metal mold having a molding face in the outercircumference and having ribs for forming the beads on the molding facealong the circumferential direction; disposing a coil forelectromagnetic forming adjacent to the outer circumference of the basering; applying a momentary large current to the coil in thisarrangement; and reducing the diameter of the base ring by pressing thebase ring toward the molding face of the metal mold such that the basering is molded into a shape corresponding to the molding face byelectromagnetic forming (so-called nosing processing).

Metal molds used for electromagnetic forming include the followings: Ametal mold having the ring-shaped molding face in the innercircumference and having the grooves for forming the beads on themolding face along the circumferential direction, and a metal moldhaving the ring-shaped molding face in the outer circumference andhaving the ribs for forming the beads on the molding face along thecircumferential direction and grooves at both sides of the ribs.

Desirable materials for the base ring include copper, copper alloys,aluminum, and aluminum alloys that have high electrical conductivity.Moreover, in terms of the quality of these materials, annealed materials(type O defined by JIS H0001 for aluminum or aluminum alloys) andhot-worked materials (type F defined by JIS H0001 for the same) aredesirable. Both of these materials have high electrical conductivity.Furthermore, the hot-worked materials are available at lower cost. Ingeneral, aluminum alloys have high electrical conductivity andrelatively high strength. In particular, aluminum alloys of JIS 6000series, especially, type 6063, type 6061, and the like are desirable.Among aluminum alloys of JIS 5000 series, type 5052 and the like areespecially desirable.

As a base ring used for electromagnetic forming, a rolled or extrudedplate roll-bended into a ring and connected at the ends, or an extrudedcylindrical material cut to a predetermined length (length in the axialdirection of extrusion) is available.

The thickness of the extruded plate can be arbitrarily set. Accordingly,the thickness of the cylindrical ring after electromagnetic forming canbe made uniform by thickening the plate at positions to be thinned afterflaring or nosing by electromagnetic forming (the positions of the beadsand the vicinity in flaring, and the positions of the grooves at bothsides of the beads and the vicinity in nosing) in advance.

Furthermore, a rolled or extruded plate spirally roll-bended into a tubeand connected at the joints is also available to the cylindrical ring.In this case, a long spiral tube may be produced and cut to a requiredlength as the cylindrical ring.

When the cylindrical ring is formed by welding, butt welding having nooverlapped portion is desirable. In the case of lap welding, a minutegap between the overlapped portions is unavoidable, and thus a spark maybe generated at the gap during electromagnetic forming to prevent normalelectromagnetic forming.

Available welding methods include resistance welding, metal inert gas(MIG) welding, laser welding, friction stir welding (FSW), and the like.Although a variety of profiles can be employed for a groove of the buttjoint, a profile having a uniform thickness over the circumference isdesirable, and a profile having a thickness thinned after connecting atthe connecting portion is especially undesirable. On the contrary, anextra reinforcement of a weld must be removed. Accordingly, laserwelding having a small reinforcement of a weld is preferable.

During electromagnetic forming, loads are repeatedly applied to aworkpiece in a very short time. Thus, the workpiece shaped byelectromagnetic forming has excellent shape-fixability (smallspringback), and a highly accurate cylindrical ring with beads can beproduced so as to achieve accurate circularity. In particular, when thering is molded by expanding the diameter in the radial direction, highercircularity can be achieved compared with that of the ring molded byreducing the diameter. Furthermore, work hardening through theelectromagnetic forming is more remarkable compared with the knownmethod. Accordingly, the beads (in particular, top portions of thebeads) are strengthened by the work hardening.

Applications of the cylindrical ring include a reinforced ring for arun-flat tire. The reinforced ring requires high circularity. Sincetreads (portions that are in contact with the ground through tires)correspond to the top portions of the beads, the cylindrical ring havinghigh circularity and strengthened beads (i.e. flared by electromagneticforming) is especially suitable for the reinforced ring. A plate ofaluminum or an aluminum alloy having a thickness of 3 mm or less is usedas the reinforced ring.

When an extruded cylindrical material is used for producing thecylindrical ring, the cylindrical ring does not have any connectingportions. However, the cylindrical ring normally has at least oneconnecting portion, desirably a connecting portion by butt welding. Thisconnecting portion is formed parallel to or inclined to the axialdirection.

Next, features of the methods for manufacturing the cylindrical ringwith the beads according to the present invention will now be described.

The molding face of the metal mold is symmetrical with respect to aplane vertical to the axial direction at the central position of theaxial direction. Furthermore, the central position of the base ring inthe axial direction desirably corresponds to that of the molding face ofthe metal mold in the axial direction. The length of the base ring inthe axial direction is reduced when the base ring is molded by flaringor nosing by electromagnetic forming (since portions of the ring areattracted into the grooves on the molding face). However, thepossibility of more uniform reduction and molding of the base ring isincreased with the molding face described as above. The axial directionof the molding face of the metal mold corresponds to that of the basering.

Preferably, the grooves on the metal mold according to the presentinvention have holes communicating with the exterior of the grooves.That is to say, vents or slits for degassing are formed in the grooves.Since molding is completed in a very short time of approximately a fewhundred microseconds in electromagnetic forming, air left in gapsbetween the molding face and the base ring cannot escape during molding.Therefore, the air is trapped and highly pressurized in the gaps betweenthe molding face and the portions pressed thereto at the grooves. Thehighly pressurized air prevents the portions from being pressed towardthe molding face at the grooves, and causes problems such as hollowscreated on the surfaces of the beads after electromagnetic forming. Thisproblem can be solved by forming vents or slits for degassing in thegrooves.

Preferably, the metal mold according to the present invention is formedof a plurality of pieces separable in the circumferential direction.With this structure, the cylindrical ring can easily be removed from themetal mold after molding.

Preferably, when the metal mold having the ring-shaped molding face inthe inner circumference and having the grooves for forming the beads onthe molding face along the circumferential direction is used forelectromagnetic forming, the metal mold according to the presentinvention is formed of a plurality of mold segments separable in theaxial direction at the grooves, and a gap is provided between twoadjacent mold segments in the axial direction. When the metal moldhaving the ring-shaped molding face in the outer circumference andhaving the ribs for forming the beads on the molding face along thecircumferential direction and the grooves at both sides of the ribs isused for electromagnetic forming, the metal mold according to thepresent invention is formed of a plurality of mold segments separable inthe axial direction at the grooves, and a gap is provided between twoadjacent mold segments in the axial direction. With these structures,slits are formed at the grooves over the entire circumference of themetal mold, and thus the problem of dents is completely solved. Theaxial direction herein means a direction of an axis of the molding faceof the metal mold (or the cylindrical ring).

Preferably, when a dimensional accuracy is insufficient after moldingthe cylindrical ring by electromagnetic forming (flaring or nosing), thecylindrical ring is corrected by, for example, roll-correcting such thatthe dimensional accuracy of the beads and the like is improved. That isto say, an inner roll and an outer roll of which outer dimensions arefinished with a required accuracy are prepared, and the cylindrical ringmolded into the shape corresponding to the molding face byelectromagnetic forming is corrected by rotating the rolls whileinterposing the cylindrical ring between the inner roll and the outerroll.

Preferably, the step of applying the momentary large current to the coilis repeated a plurality number of times such that the dimensionalaccuracy is improved. In this case, electromagnetic forming (nosing) maybe performed after electromagnetic forming (flaring), or the formingoperations may be inversely preformed. Alternatively, the same formingoperation of flaring or nosing may be repeated a plurality number oftimes. In all cases, the second and subsequent electromagnetic formingoperations are regarded as correcting operations.

Preferably, the metal mold has a circular cutting blade between each ofmolding faces corresponding to the cylindrical rings, and the cuttingblade can cut the base ring when the base ring is pressed toward themolding faces of the metal mold. As a result, a plurality of cylindricalrings with beads can be produced at one time by electromagnetic forming(flaring or nosing). In this case, the metal mold must have theplurality of molding faces each corresponding to a cylindrical ring inthe axial direction, and the coil for the electromagnetic forming alsorequires a length corresponding to the molding faces in the axialdirection. In this case, the plurality of cylindrical rings can beseparated at the same time as the electromagnetic forming, and thus theproductivity is improved.

Preferably, when the plurality of cylindrical rings are produced at onetime but are not separated in the metal mold, rolls with cutting bladescan be used to separate the cylindrical rings at the same time asroll-correcting in the same manner as the roll-correcting.

Preferably, the base ring according to the present invention has a largenumber of holes in the circumferential wall. These holes are preferablyarranged in the circumference wall in a regular manner. The cylindricalring can be reduced in weight by forming the plurality of holes in thecircumference wall. The cylindrical ring can be effectively reduced inweight when the holes are formed in the approximately overallcircumferential wall of the base ring in a regular manner. Such a basering includes, for example, a ring produced by roll-bending a perforatedmetal and by connecting the ends, and a ring produced by spirallywinding a perforated metal and by connecting the joints by welding.

In electromagnetic forming, the base ring is pressed into the grooves ofthe molding face of the metal mold, and thus the base ring transfers inthe axial direction along the molding face of the metal mold. At thistime, strong frictional resistance occurs between the molding face ofthe metal mold and the base ring. The formation of the plurality ofholes in the base ring can reduce the contact area between the metalmold and the base ring that come into contact with each other inelectromagnetic forming, and can reduce the frictional resistancetherebetween. As a result, the base ring can smoothly enter the interiorof the grooves from the exterior of the grooves of the molding face ofthe metal mold, resulting in more accurate molding. In particular, thelarge number of holes are effective when formed in the circumferentialwall of the base ring along the circumferential direction at positionswhere portions of the base ring enter the interior of the grooves fromthe exterior of the grooves of the molding face of the metal mold inelectromagnetic forming. In general, these positions are at both endportions of the base ring in the axial direction.

Preferably, positioning holes during electromagnetic forming are formedin the base ring. For the cylindrical ring molded by electromagneticforming (flaring), a large number of projections are formed in themolding face of the metal mold along the circumferential direction atpositions where the internal diameter of the molding face is thesmallest, a large number of holes are formed in the base ring along thecircumferential direction at positions corresponding to the projections,and the projections are fitted into the holes when the metal mold isdisposed adjacent to the outer circumference of the base ring. In thiscase, the projections are desirably formed between two adjacent grooveson the molding face at the central position of the molding face of themetal mold in the axial direction, and also, the holes are desirablyformed at the central position of the base ring in the axial direction.

For the cylindrical ring molded by electromagnetic forming (nosing), alarge number of projections are formed in the molding face of the metalmold along the circumferential direction at positions where the externaldiameter of the molding face is the largest, a large number of holes areformed in the cylindrical ring along the circumferential direction atpositions corresponding to the projections, and the projections arefitted into the holes when the metal mold is disposed adjacent to theinner circumference of the cylindrical ring. In this case, theprojections are desirably formed on the ribs on the molding face at thecentral position of the molding face of the metal mold in the axialdirection, and also, the holes are preferably formed at the centralposition of the base ring in the axial direction.

With these structures, the base ring is accurately positioned in themetal mold, and the base ring fixed by these positioning holes also doesnot transfer in the axial direction during electromagnetic forming.

Preferably, the base ring is in contact with the molding face of themetal mold at the central position of the molding face of the metal moldin the axial direction before electromagnetic forming. That is to say,in flaring, the internal diameter at the central position of the moldingface of the metal mold in the axial direction is the smallest, and theouter circumference of the base ring is in contact with the molding faceof the metal mold at the corresponding position. With this structure,the base ring is positioned at the corresponding position at molding,and thus more uniform molding can be performed. On the contrary, innosing, the external diameter at the central position of the moldingface of the metal mold in the axial direction is the largest, and theinner circumference of the base ring is in contact with the molding faceof the metal mold at the corresponding position. In both cases, thecentral position of the molding face of the metal mold in the axialdirection desirably corresponds to that of the base ring in the axialdirection.

Meanwhile, the holes formed in the base ring can be used to connect themolded cylindrical ring with other members. For example, in a reinforcedring for a run-flat tire, resin is attached to the reinforced ring atboth end portions in the axial direction. At this time, the resin flowsinto the holes such that the connection between the reinforced ring andthe resin becomes more secure.

In addition, the cylindrical ring molded by electromagnetic forming canbe cut off in the circumferential direction, if necessary. The cuttingdirection is preferably parallel to or inclined to the axial directionof the cylindrical ring, for example. Two of such cylindrical rings canbe linked together through respective cut-off portions (splits), andthus only a small space is required for storage or transportation.Furthermore, the cut-off portion of the cylindrical ring can bereconnected so as to close the ring again. For the reconnection bywelding, butt welding is desirable, and in particular, laser weldinghaving a small reinforcement of a weld is preferable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) and 1(b) are a side view and a front view, respectively, of abase ring before electromagnetic forming.

FIGS. 2(a), 2(b), and 2(c) are a cross-sectional view, a side view, anda front view, respectively, of a cylindrical ring with beads afterelectromagnetic forming.

FIGS. 3(a) and 3(b) are cross-sectional views before and after molding,respectively, illustrating a method for manufacturing a cylindrical ringwith beads by electromagnetic forming.

FIGS. 4(a), 4(b), and 4(c) are a side view, a cross-sectional view, anda partly enlarged view of the cross-sectional view, respectively,illustrating an exemplary structure of a metal mold for electromagneticforming.

FIGS. 5(a) and 5(b) are cross-sectional views before and after molding,respectively, illustrating a method for manufacturing a cylindrical ringwith beads by electromagnetic forming.

FIGS. 6(a) and 6(b) are a sectioned side view and a sectioned frontview, respectively, illustrating a method for correcting a cylindricalring with beads.

FIGS. 7(a) and 7(b) are cross-sectional views before and aftercorrecting, respectively, illustrating the method for correcting thecylindrical ring.

FIGS. 8(a), 8(b), and 8(c) are cross-sectional views before molding,after a first-step molding, and a second-step molding, respectively,illustrating a method for molding a cylindrical ring with beads withmultiple steps.

FIG. 9 is a cross-sectional view illustrating a method for manufacturinga plurality of cylindrical rings with beads at one time.

FIGS. 10(a) and 10(b) are a sectioned side view and a sectioned frontview, respectively, illustrating a method for separating and correctingthe connected cylindrical rings.

FIG. 11 is a front view of another base ring used for the presentinvention.

FIG. 12 is a front view of another base ring used for the presentinvention.

FIGS. 13(a) and 13(b) are cross-sectional views before and aftermolding, respectively, illustrating a method for manufacturing acylindrical ring with beads using the above-described base ring.

FIG. 14 is a front view of another base ring used for the presentinvention.

FIGS. 15(a) and 15(b) are cross-sectional views before and aftermolding, respectively, illustrating a method for manufacturing acylindrical ring with beads using the above-described base ring.

FIG. 16 is a front view of another base ring used for the presentinvention.

FIG. 17(a) is a front view of a cylindrical ring with beads molded usingthe above-described base ring, and FIG. 17(b) is a cross-sectional viewillustrating a state after the cylindrical ring is connected by resin.

FIGS. 18(a) and 18(b) are perspective views of cylindrical rings withbeads cut off in the circumferential direction.

FIGS. 19(a) and 19(b) are perspective views of the cylindrical ringsreconnected by welding after being cut off.

FIGS. 20(a) and 20(b) are a side view and a cross-sectional view takenalong line A-A in FIG. 20(a), respectively, of the cylindrical ringreconnected by rivets after being cut off.

FIGS. 21(a) and 21(b) are a side view and a cross-sectional view takenalong line A-A in FIG. 21(a), respectively, of the cylindrical ringreconnected by resin after being cut off.

FIGS. 22(a) and 22(b) are a side view and a cross-sectional view takenalong line A-A in FIG. 22(a), respectively, of the cylindrical ringreconnected by resin after being the cut off.

FIGS. 23(a) and 23(b) are schematic views illustrating the arrangementof the holes and gaps between two adjacent hole lines when a cylindricalring with beads having a large number of holes is cut off in thecircumferential direction.

FIGS. 24(a) and 24(b) are cross-sectional views before and aftermolding, respectively, illustrating a method for manufacturing acylindrical ring with beads by electromagnetic forming.

FIGS. 25(a) to 25(d) illustrate methods for producing base rings.

BEST MODE FOR CARRYING OUT THE INVENTION

Methods for manufacturing a cylindrical ring with beads according to thepresent invention and the resultant cylindrical ring with the beads willnow be described in detail with reference to FIGS. 1 to 25.

A base ring 1 shown in FIG. 1 is formed by roll-bending a plate of, forexample, an aluminum alloy and by butt welding the ends. A referencenumeral 2 denotes a connecting portion formed by the butt welding.

FIG. 3 illustrates a method for molding the base ring 1 byelectromagnetic forming (flaring). In FIG. 3(a), a metal mold 6 isdisposed adjacent to the outer circumference of the base ring 1, and hasa molding face in the inner circumference and grooves 3 to 5 for formingbeads on the molding face along the circumferential direction. A coilcomponent 7 for electromagnetic forming is disposed adjacent to theinner circumference of the base ring 1. The molding face of the metalmold 6 is substantially rotationally symmetrical with respect to thecentral axis (although the molding face is not rotationally symmetricalwith respect to the central axis in the strict sense of the word due to,for example, vents 11 (described below), the molding face can besubstantially regarded to be rotationally symmetrical with respect tothe central axis in terms of the functionality), and is substantiallysymmetrical with respect to a plane vertical to the axial direction atthe central position of the axial direction. Moreover, the centralposition of the molding face of the metal mold 6 in the axial directioncorresponds to that of the base ring 1 in the axial direction. Smallgaps are provided between the outer circumference of the base ring 1 andthe inner circumference of the metal mold 6, and between the innercircumference of the base ring 1 and the coil component 7.

The metal mold 6 is desirably composed of a metal with low electricalconductivity such as stainless steel. Materials other than metals, forexample, structural materials having no electrical conductivity such asfiber-reinforced plastic or bakelite can also be employed. The grooves 3to 5 formed on the molding face (inner circumference) of the metal mold6 extend in the radial direction, and are undulated abreast with eachother. Ends of the grooves 3 and 5 are connected to parallel endportions 8 and 9 of the molding face, respectively. Moreover, a largenumber of vents 11 for degassing are formed in bottom portions of thegrooves 3 to 5 along the circumferential direction. The vents 11 may belong slits formed along the circumferential direction. The coilcomponent 7 is formed of a molding coil 7 a embedded in an electricalinsulator.

When a momentary large current is applied to the coil component 7 in thestate shown in FIG. 3(a), a force by magnetic repulsion is generated atthe base ring 1. The diameter of the base ring 1 is then expanded, andthe base ring 1 is pressed toward the molding face of the metal mold 6at that moment. Thus, as shown in FIG. 3(b), the base ring 1 is moldedinto a shape along the molding face so as to be a cylindrical ring 17with beads. The cylindrical ring 17 includes short parallel portions 12and 13 at both ends in the axial direction and three beads 14 to 16(that are undulated abreast with each other) convexed in the radialdirection along the circumferential direction between the parallelportions 12 and 13 (See FIG. 2 for a detailed shape). The cylindricalring 17 is substantially rotationally symmetrical with respect to thecentral axis, and is substantially symmetrical with respect to a planevertical to the axial direction at the central position of the axialdirection. The base ring 1 is attracted to the grooves 3 to 5 by theelectromagnetic forming, and as a result, the width of the cylindricalring 17 in the axial direction is made smaller than the width of thebase ring 1 in the axial direction.

The metal mold 6 is formed of a plurality of pieces separable in thecircumferential direction (See separable pieces 25 a and 25 b of aseparable mold segment 25) such that the cylindrical ring 17 can beremoved from the metal mold 6 after molding.

FIG. 4 illustrates an exemplary structure of a metal mold including aplurality of mold segments separable in the axial direction. This metalmold 21 has a molding face in the inner circumference, and grooves 22 to24 for forming beads on the molding face along the circumferentialdirection. The metal mold 21 is formed of a plurality of ring-shapedseparable mold segments 25 to 28 separable in the axial direction at thegrooves 22 to 24. The separable mold segments 25 to 28 are disposed withring-shaped spacers 29 to 31 interposed therebetween. As a result, gaps32 to 34 are provided between two adjacent separable mold segments 25 to28.

Furthermore, the separable mold segment 25 (the same applies to theseparable mold segments 26 to 28) is formed of a plurality of separablepieces 25 a and 25 b (in some cases, two or more separable pieces)separable in the circumferential direction and linked by bolts 35 andcatching pieces 36.

In FIG. 4, a reference numeral 37 denotes a bolt for fixing theseparable mold segments 25 to 28, and a reference numeral 38 denotes anut.

In this metal mold 21, the separable mold segments 25 to 28 each has acurved molding face being part of the grooves 22 to 24, and the moldingfaces and the gaps 32 to 34 disposed in the middle portions thereof (thebottom portions of the grooves 22 to 24) form the grooves 22 to 24. Inother words, the groove 22 is formed of the curved molding faces of twoadjacent separable mold segments 25 and 26 and the gap 32 in the middleportion, the groove 23 is formed of the curved molding faces of twoadjacent separable mold segments 26 and 27 and the gap 33 in the middleportion, and the groove 24 is formed of the curved molding faces of twoadjacent separable mold segments 27 and 28 and the gap 34 in the middleportion. The molding faces of the metal mold 21 are substantiallyrotationally symmetrical with respect to the central axis, and aresubstantially symmetrical with respect to a plane vertical to the axialdirection at the central position of the axial direction. The gaps 32 to34 are formed in the respective grooves 22 to 24 over the entirecircumference, and function as slits for degassing duringelectromagnetic forming.

A base ring is disposed adjacent to the inner circumference of the metalmold 21 such that the central position of the molding face of the metalmold 21 in the axial direction corresponds to the central position ofthe base ring in the axial direction. In addition, a coil component forelectromagnetic forming is disposed adjacent to the inner circumferenceof the base ring. When electromagnetic forming is performed with thisarrangement, the diameter of the base ring is expanded, and the basering is pressed toward the molding face of the metal mold 21 (theseparable mold segments 25 to 28) at that moment as in the case shown inFIGS. 1 and 3. Thus, the base ring is molded into a shape along themolding face, whereas the base ring is freely deformed at the gaps 32 to34 (the bottom portions of the grooves 22 to 24) in response to loadsapplied to the base ring. In short, top portions of beads of acylindrical ring are formed in these gaps 32 to 34 (the bottom portionsof the grooves 22 to 24). By appropriately setting the widths of thegaps 32 to 34, degassing can be successfully performed, and the ring canbe deformed at these gaps 32 to 34 into a shape substantially alongcurved lines (See a virtual line E shown in FIG. 4(c)) formed byinterpolating the molding faces of two adjacent separable mold segmentsinterposed by the gaps 32 to 34. The resultant cylindrical ring with thebeads is substantially rotationally symmetrical with respect to thecentral axis, and is substantially symmetrical with respect to a planevertical to the axial direction at the central position of the axialdirection.

FIG. 5 illustrates a method for molding the base ring 1 byelectromagnetic forming (nosing). In FIG. 5(a), a metal mold 44 isdisposed adjacent to the inner circumference of the base ring 1; and hasa molding face in the outer circumference, ribs 41 and 42 for formingbeads on the molding face along the circumferential direction, andgrooves 43 a to 43 c at both sides of the ribs. A coil component 45 forelectromagnetic forming is disposed adjacent to the outer circumferenceof the base ring 1. Small gaps are provided between the innercircumference of the base ring 1 and the outer circumference of themetal mold 44, and between the outer circumference of the base ring 1and the coil component 45.

The ribs 41 and 42 formed on the molding face (outer circumference) ofthe metal mold 44 protrude in the radial direction and the grooves 43 ato 43 c extend in the radial direction. These ribs 41 and 42 and thegrooves 43 a to 43 c are undulated abreast with each other, and ends ofthe grooves 43 a and 43 c are connected to parallel end portions 46 and47 of the molding face, respectively. The molding face of the metal mold44 is substantially rotationally symmetrical with respect to the centralaxis, and is substantially symmetrical with respect to a plane verticalto the axial direction at the central position of the axial direction.Moreover, the central position of the molding face of the metal mold 44in the axial direction corresponds to that of the base ring 1 in theaxial direction. As in the case shown in FIG. 3, vents or slits 48 fordegassing are formed in bottom portions of the grooves 43 a to 43 c.

When a momentary large current is applied to the coil component 45 inthe state shown in FIG. 5(a), a force by magnetic repulsion is generatedat the base ring 1. The diameter of the base ring 1 is then reduced, andthe base ring 1 is pressed toward the molding face of the metal mold 44at that moment. Thus, as shown in FIG. 5(b), the base ring 1 is moldedinto a shape along the molding face so as to be a cylindrical ring 56with beads. The cylindrical ring 56 includes short parallel portions 51and 52 at both ends and two beads 53 and 54 (grooves 55 a to 55 c areformed at both sides of the respective beads, and are undulated abreastwith the beads 53 and 54) convexed in the radial direction along thecircumferential direction between the parallel portions 51 and 52. Thiscylindrical ring 56 is substantially rotationally symmetrical withrespect to the central axis, and is substantially symmetrical withrespect to a plane vertical to the axial direction at the centralposition of the axial direction. The base ring 1 is attracted to thegrooves 43 a to 43 c by the electromagnetic forming, and as a result,the width of the cylindrical ring 56 in the axial direction is madesmaller than the width of the base ring 1 in the axial direction.

The metal mold 44 is formed of a plurality of pieces separable in thecircumferential direction such that the cylindrical ring 54 can beremoved from the metal mold 44 after molding.

FIG. 6 illustrates a method for roll-correcting to improve dimensionalaccuracy of a cylindrical ring 57 with beads after electromagneticforming (flaring or nosing). It may be performed, for example, when adent is created on a bead due to insufficient degassing, or when theaccuracy of a top portion of a bead that is freely deformed is low afterelectromagnetic forming using a type of the metal mold shown in FIG. 4.

The roll-correcting is performed by holding the cylindrical ring 57between an inner roll 58 and outer rolls 59 of which outer dimensionsare finished with a required accuracy, and by rotating the rolls whileadjusting the shift of the inner roll 58.

FIG. 7 illustrates a method for correcting by additional electromagneticforming (nosing) to improve dimensional accuracy of a cylindrical ring61 with beads molded by electromagnetic forming (flaring). It may beperformed, for example, when a dent is created on a bead due toinsufficient degassing, or when the accuracy of a top portion of a beadthat is freely deformed is low after electromagnetic forming using atype of the metal mold shown in FIG. 4. In this case, the diameter ofthe cylindrical ring 61 is expanded slightly larger than that in thefinal shape.

As shown in FIG. 7(a), a metal mold 65 is disposed adjacent to the innercircumference of the cylindrical ring 61 that is molded byelectromagnetic forming (flaring) in advance, and has a molding facecorresponding to the final shape in the outer circumference andprotrusions 62 to 64 for correcting on the molding face along thecircumferential direction. A coil component 66 for electromagneticforming is disposed adjacent to the outer circumference of thecylindrical ring 61. The molding face of the metal mold 65 issubstantially rotationally symmetrical with respect to the central axis.A reference numeral 67 denotes a vent or a slit for degassing.Furthermore, the metal mold 65 is formed of a plurality of piecesseparable in the circumferential direction as in the case describedabove.

As shown in FIG. 7(b), when a momentary large current is applied to thecoil component 66 in the state, electromagnetic forming (nosing) isperformed as in the case shown in FIG. 5. Thus, the cylindrical ring 61is molded, i.e. corrected, into a shape along the molding face of themetal mold 65 so as to be a cylindrical ring 69 with beads having a highdimensional accuracy.

FIG. 8 illustrates a multi-step process for obtaining a cylindrical ringwith beads having a high dimensional accuracy by repeatingelectromagnetic forming.

First, as shown in FIG. 8(a), a metal mold 74 is disposed adjacent tothe outer circumference of the base ring 1, and has a molding face inthe inner circumference and grooves 71 to 73 for forming beads on themolding face along the circumferential direction. A coil component 75for electromagnetic forming is disposed adjacent to the innercircumference of the base ring 1. The molding face of the metal mold 74is substantially rotationally symmetrical with respect to the centralaxis. A large number of vents or slits 76 for degassing are formed inbottom portions of the grooves 71 to 73. Moreover, the metal mold 74 isformed of a plurality of pieces separable in the circumferentialdirection.

When a momentary large current is applied to the coil component 75 inthe state shown in FIG. 8(a), the diameter of the base ring 1 isexpanded, and the base ring 1 is pressed toward the molding face of themetal mold 74 at that moment. However, the electrical energy applied tothe coil component 75, i.e. the force by magnetic repulsion generated atthe base ring 1, at this time is not set so large. Accordingly, as shownin FIG. 8(b), the base ring 1 is not molded into a shape sufficientlyalong the molding face (in particular, the grooves 71 to 73) of themetal mold 74. That is to say, the base ring 1 is attracted to thegrooves 71 to 73 so as to be convexed, whereas gaps are formed between amolded cylindrical ring 77 with beads and the molding face (inparticular, the grooves 71 to 73) of the metal mold 74. Therefore, evenwhen air is shut in the gaps due to insufficient degassing, this doesnot lead to an extremely high pressure, and the problem of the dents isreduced.

Next, as shown in FIG. 8(c), electromagnetic forming is performed again,and the cylindrical ring 77 is molded into the shape along the moldingface (in particular, the grooves 71 to 73) of the metal mold 74, i.e.the final shape this time. This molding can be regarded as a sort ofcorrection.

In this embodiment, the force by magnetic repulsion is generated moreeffectively by using a coil component 78 for electromagnetic forminghaving a larger coil diameter. A cylindrical ring 79 with beads isformed into a shape along the molding face of the metal mold 74 aftermolding, and is in almost close contact with the molding face. Since thevolume of the air possibly shut in the grooves 71 to 73 is smallcompared with the molding of the base ring 1 into the cylindrical ring79 in one step, the pressure is not excessively increased even withinsufficient degassing, and the problem of the dents is resolved.

In this embodiment, although two-step molding is performed by using thesame metal mold 74, different metal molds (for preliminary molding andfor finishing) may also be used. In that case, the base ring may bemolded into a shape along the molding face of the metal mold forpreliminary molding in the first molding step.

FIG. 9 illustrates a method for molding a plurality of (in thisembodiment, two) cylindrical rings with beads in one step. A metal mold82 is disposed adjacent to the outer circumference of a base ring 81having a length corresponding to two rings, and has a molding face inthe inner circumference. A coil component 83 for electromagnetic formingis disposed adjacent to the inner circumference of the base ring 81. Twosets of grooves 84 to 86 for forming beads are formed on the moldingface of the metal mold 82 along the circumferential direction abreast inthe axial direction. A circular cutting blade 87 is disposed inward inthe intermediate position of the metal mold 82. A large number of ventsor slits 88 for degassing are formed in bottom portions of the grooves84 to 86 along the circumferential direction. Moreover, The metal mold82 is formed of a plurality of pieces separable in the circumferentialdirection.

When a momentary large current is applied to the coil component 83 inthe state shown in FIG. 9, a force by magnetic repulsion is generated atthe base ring 81. The diameter of the base ring 1 is then expanded, andthe base ring 1 is pressed toward the molding face of the metal mold 82at that moment. Thus, the base ring 81 is molded into a shape along themolding face, and at the same time, is separated at the intermediateposition by the cutting blade. As a result, two rings same as thecylindrical ring 17 shown in FIG. 3(b) can be produced at one time.

When there is no cutting blade 87 in the metal mold 82 shown in FIG. 9,the resultant cylinder with beads includes a plurality of cylindricalrings with beads linked together.

FIG. 10 illustrates a method for roll-correcting and cutting to improvedimensional accuracy of such a cylinder 91 with beads including aplurality of (two) cylindrical rings with beads linked together, and atthe same time, to separate the cylinder 91 into a plurality of (two)individual cylindrical rings. The method for roll-correcting isbasically the same as that shown in FIG. 6. However, in this case, acutting blade 93 is formed in the intermediate position of an inner roll92, and receiving blades 95 for the cutting blade 93 are formed inrespective positions of outer rolls 94. The roll-correcting and cuttingis performed by holding the cylinder 91 between the inner roll 93 andthe outer rolls 94, and by rotating the rolls while the inner roll 93 isshifted.

FIG. 11 illustrates a base ring 101 having a large number of holes 102formed over the entire surface of the circumferential wall. This basering 101 can be produced by roll-bending a rectangular metal plate (forexample, a plate of an aluminum alloy) having the holes 102 regularlyarranged in a grid, i.e. a perforated metal, and by connecting the endsby welding or the like.

When the base ring 101 is molded by electromagnetic forming using, forexample, the metal mold 6 and the coil component 7 shown in FIG. 3, alighter cylindrical ring with beads can be produced. Since the largenumber of holes 102 are formed over the entire surface of the base ring101, the degassing vents or slits formed in the metal mold 6 and thelike, and the degassing gaps formed in the metal mold 21 (See FIG. 4)are unnecessary.

FIG. 12 illustrates a base ring 103 having a large number of holes 102formed in the circumferential wall along the circumferential directionat both end portions in the axial direction in a symmetric manner. Theseholes 102 are arranged in two hole lines (an outer hole line 102 a andan inner hole line 102 b) making a circuit of the circumferential wallat both end portions in the axial direction, and are disposed at regularintervals in the hole lines 102 a and 102 b. This base ring 103 can beproduced by roll-bending a rectangular metal plate (for example, a plateof an aluminum alloy) having the plurality of holes 102 arranged in twolines in parallel adjacent to the end portions in the axial directionalong the circumferential direction, and by connecting the ends bywelding or the like.

FIG. 13 illustrates a method for molding this base ring 103 byelectromagnetic forming. In FIG. 13(a), a metal mold 106 (formed of aplurality of pieces separable in the circumferential direction as in thecase for the metal mold 6) is disposed adjacent to the outercircumference of the base ring 103, and has a molding face in the innercircumference and grooves 104 and 105 for forming beads on the moldingface along the circumferential direction. A coil component 107 forelectromagnetic forming is disposed adjacent to the inner circumferenceof the base ring 103. The molding face of the metal mold 106 issubstantially rotationally symmetrical with respect to the central axis,and is substantially symmetrical with respect to a plane vertical to theaxial direction at the central position of the axial direction.Moreover, the central position of the molding face of the metal mold 106in the axial direction corresponds to that of the base ring 103 in theaxial direction.

When a momentary large current is applied to the coil component 107 inthe state shown in FIG. 13(a), a force by magnetic repulsion isgenerated at the base ring 103. The diameter of the base ring 103 isthen expanded, and the base ring 103 is pressed toward the molding faceof the metal mold 106 at that moment. Thus, as shown in FIG. 13(b), thebase ring 103 is molded into a shape along the molding face so as to bea cylindrical ring 113 with beads. The cylindrical ring 113 includesshort parallel portions 108 and 109 at both ends in the axial directionand two beads 111 and 112 (the beads 111 and 112 are undulated abreastwith each other) convexed in the radial direction along thecircumferential direction between the parallel portions 108 and 109.This cylindrical ring 113 is substantially rotationally symmetrical withrespect to the central axis (although the cylindrical ring is notrotationally symmetrical with respect to the central axis in the strictsense of the word due to, for example, the holes 102, the cylindricalring can be substantially regarded to be rotationally symmetrical withrespect to the central axis in consideration of the profile thereof),and is substantially symmetrical with respect to a plane vertical to theaxial direction at the central position of the axial direction.

The base ring 103 is pressed into the grooves 104 and 105 by theelectromagnetic forming, and as a result, portions of the base ring 103located at outer positions of the grooves 104 and 105 in the axialdirection enter the grooves 104 and 105. Before molding, the holes 102of the base ring 103 in both hole lines (the hole lines 102 a and 102 b)are located at the outer positions of the grooves 104 and 105 of themolding face of the metal mold 106. However, when the portions of thebase ring 103 at both ends enter the grooves 104 and 105, the hole lines102 b are located in the grooves 104 and 105. In other words, in thebase ring 103, the hole lines 102 b disposed at the inner positions inthe axial direction are located on the beads 111 and 112, and the holelines 102 a disposed at the outer positions in the axial direction arelocated adjacent to borders between the parallel portion 108 and thebead 111 and between the parallel portion 109 and the bead 112.

When the end portions of the base ring 103 enter the grooves 104 and 105from the parallel end portions of the metal mold 106, frictionalresistance between the molding face of the metal mold 106 and the basering 103 is reduced since the contact area therebetween is reduced dueto the holes 102 compared with the base ring 1 and the like having noholes. As a result, the base ring 103 can smoothly enter the grooves 104and 105, and the electromagnetic forming can be accurately performed.Substantially the same effect as this can be accomplished also with thebase ring 101.

FIG. 14 illustrates a base ring 115 having a line of a large number ofholes 102 formed in the middle position in the axial direction along thecircumferential direction at regular intervals. This base ring 115 canbe produced by roll-bending a rectangular metal plate (for example, aplate of an aluminum alloy) having the plurality of holes 102 disposedin one line, and by connecting the ends by welding or the like.

FIG. 15 illustrates a method for molding this base ring 115 byelectromagnetic forming. In FIG. 15(a), a metal mold 116 (formed of aplurality of pieces separable in the circumferential direction as in thecase for the metal mold 6) is disposed adjacent to the outercircumference of the base ring 115, and has a molding face in the innercircumference and grooves 117 and 118 for forming beads on the moldingface along the circumferential direction. The intermediate portion 119between the grooves 117 and 118 protrudes inward, and projections 121are formed along the circumferential direction at the top of theintermediate portion 119 where the internal diameter is the smallest atregular intervals. The molding face of the metal mold 116 issubstantially rotationally symmetrical with respect to the central axis(although the molding face is not rotationally symmetrical with respectto the central axis in the strict sense of the word due to, for example,projections 121, the molding face can be substantially regarded to berotationally symmetrical with respect to the central axis in terms ofthe functionality), and is substantially symmetrical with respect to aplane vertical to the axial direction at the central position of theaxial direction.

The intervals between two adjacent projections 121 of the metal mold 116correspond to the intervals between two adjacent holes 102 of the basering 115. Also, when the metal mold 116 is disposed around the base ring115, the internal diameter of the top of the intermediate portion 119substantially corresponds to the external diameter of the base ring 115such that the projections 121 are fitted in the holes 102, and themolding face of the metal mold 116 is in contact with the outercircumference of the base ring 115 at the top of the intermediateportion 119.

When a momentary large current is applied to a coil component 122 forelectromagnetic forming in the state shown in FIG. 15(a), a force bymagnetic repulsion is generated at the base ring 115. The diameter ofthe base ring 115 is then expanded, and the base ring 115 is pressedtoward the molding face of the metal mold 116 at that moment. Thus, asshown in FIG. 15(b), the base ring 115 is molded into a shape along themolding face so as to be a cylindrical ring 127 with beads. Thecylindrical ring 127 includes short parallel portions 123 and 124 atboth ends in the axial direction and two beads 125 and 126 (both thebeads 125 and 126 are undulated abreast with each other) convexed in theradial direction along the circumferential direction between theparallel portions 123 and 124. This cylindrical ring 127 issubstantially rotationally symmetrical with respect to the central axis,and is substantially symmetrical with respect to a plane vertical to theaxial direction at the central position of the axial direction.

The base ring 115 is accurately positioned in the metal mold 116 byfitting the projections 121 of the metal mold 116 into the holes 102 ofthe base ring 115. Accordingly, the middle portion of the base ring 115also does not move in the axial direction during electromagneticforming, and the molding can be performed accurately.

When the diameter of the base ring 115 is reduced by electromagneticforming (a metal mold is disposed inside the base ring 115), projectionsto be fitted into the holes 102 of the base ring 115 are formed atpositions where the external diameter of the molding face of the metalmold is the largest. The projections are desirably formed at the middleposition in the axial direction as in the case for the above-describedmetal mold 116. In addition, when the metal mold is disposed inside thebase ring 115, the external diameter of the molding face substantiallycorresponds to the internal diameter of the base ring 115.

The holes 102 of the base ring 101 formed in the circumferentialdirection (in particular, the hole lines in the center or adjacent tothe center) can also be available for positioning.

FIG. 16 illustrates a base ring 131 having a line of a large number ofholes 102 formed at each end portion in the axial direction along thecircumferential direction at regular intervals. A cylindrical ring 132with beads (indicated by solid lines) shown in FIG. 17(a) is produced bymolding the base ring 131 by electromagnetic forming using the metalmold 106 shown in FIG. 13. As indicated by virtual lines in FIG. 17(a),resin 133 is melted and attached to this cylindrical ring 132 at bothend portions in the axial direction. The resin 133 flows in the holes102 as shown in FIG. 17(b), and thus the cylindrical ring 132 and theresin 133 are firmly connected.

The same effect as this can be accomplished also with the base rings 101and 103.

FIGS. 18(a) and 18(b) illustrate cylindrical rings with beads that aremolded by electromagnetic forming and then cut off in thecircumferential direction. The cutting directions are parallel to theaxial direction in FIG. 18(a) and inclined to the axial direction inFIG. 18(b), respectively. These cylindrical rings 134 and 135 with beadscan be linked together through respective cut-off portions (splits 136and 137).

The cut-off portions of these cylindrical rings 134 and 135 can bereconnected by welding or the like, if necessary.

FIGS. 19(a) and 19(b) illustrate the cylindrical rings 134 and 135 thatare reconnected by welding (welds 138 and 139).

The cylindrical rings 134 and 135 may be used both in the state wherethe cylindrical rings are cut off in the circumferential direction (SeeFIG. 18) and in the state where the cut-off portions are reconnected(See FIG. 19). It is desirable in some applications that the cuttingdirection be inclined to the axial direction. For example, when thecylindrical ring 135 having the inclined cutting portion is used as areinforced ring for a run-flat tire and the length t1 of the split 137or the weld 139 in the circumferential direction is larger than thewidth t0 of a contact surface in the circumferential direction, the loadof the total car weight is not concentrated on the entire split 137 orthe entire weld 139 having relatively low strength at one time.

When a cylindrical ring with beads having a plurality of holes is cutoff in the circumferential direction and is then reconnected, theabove-described holes 102 can be used for the connection. This will bedescribed with reference to the cylindrical ring 132 as an example.

FIG. 20 illustrates the cylindrical ring 132 that is cut off in thecircumferential direction and is then connected by rivets 141 at the endportions partly overlapped. The rivets 141 pass through the overlappedholes 102 so as to connect the end portions.

FIG. 21 illustrates the cylindrical ring 132 that is cut off in thecircumferential direction and is then connected by melted resin 142 atthe end portions partly overlapped. The resin 142 flows into theoverlapped holes 102, and is cured to connect the end portions.

FIG. 22 illustrates the cylindrical ring 132 that is cut off in thecircumferential direction so as to form an open split 143 and is thenconnected by melted resin 144 at the split 143. The resin 144 flows intothe overlapped holes 102, and is cured to connect the end portions. Inthis case, the end portions may be connected by the resin 144 while thesplit 143 is closed.

When a cylindrical ring with beads having a plurality of holes is cutoff in the circumferential direction, in particular, when the cuttingline is inclined to the axial direction, it is sometimes desirable thatthe plurality of holes 102 be in a staggered arrangement (the positionsof the holes 102 of two adjacent hole lines are shifted by half a pitchin the circumferential direction) shown in FIG. 23(b) rather than a gridarrangement (See the base ring 101 in FIG. 11) shown in FIG. 23(a). Itis because, when viewing oblique hole lines formed of the plurality ofholes 102, the gaps (h2) between two adjacent hole lines in thestaggered arrangement can be made wider than the gaps (h1) in the gridarrangement (h2>h1) as shown in FIGS. 23(a) and 23(b). As a result, thecylindrical ring having the holes in the staggered arrangement can becut more easily, and can also be weld more easily when it isreconnected.

FIG. 24 illustrates a method for molding the base ring 1 byelectromagnetic forming using a metal mold 156 (formed of a plurality ofpieces separable in the circumferential direction as in the case for themetal mold 6). The metal mold 156 is similar to the metal mold 106. Themetal mold 156 has a molding face in the inner circumference, and hasgrooves 151 and 152 for forming beads on the molding face along thecircumferential direction. The intermediate portion 153 of the grooves151 and 152 protrudes inward, and the internal diameter of the moldingface is the smallest at the intermediate portion 153. The molding faceof the metal mold 156 is substantially rotationally symmetrical withrespect to the central axis, and is substantially symmetrical withrespect to a plane vertical to the axial direction at the centralposition of the metal mold 156 in the axial direction.

As shown in FIG. 24(a), the base ring 1 is disposed inside the metalmold 106, and furthermore, a coil component 157 for electromagneticforming is disposed adjacent to the inner circumference of the base ring1. The external diameter of the base ring 1 substantially corresponds tothe internal diameter of the intermediate portion 153 of the metal mold106, and the molding face of the metal mold 156 is in contact with theouter circumference of the base ring 1 in the intermediate portion 153.In addition, the central position of the molding face of the metal mold156 in the axial direction corresponds to the central position of thebase ring 1 in the axial direction.

When a momentary large current is applied to the coil component 157 inthe state shown in FIG. 24(a), a force by magnetic repulsion isgenerated at the base ring 1. The diameter of the base ring 1 is thenexpanded, and the base ring 1 is pressed toward the molding face of themetal mold 156 at that moment. Thus, as shown in FIG. 24(b), the basering 1 is molded into a shape along the molding face so as to be acylindrical ring 164 with beads. The cylindrical ring 164 includes shortparallel portions 158 and 159 at both ends in the axial direction andtwo beads 161 and 162 (both the beads 161 and 162 are undulated togetherwith a small-diameter portion 163 therebetween) convexed in the radialdirection along the circumferential direction between the parallelportions 158 and 159. This cylindrical ring 164 is substantiallyrotationally symmetrical with respect to the central axis, and issubstantially symmetrical with respect to a plane vertical to the axialdirection at the central position of the axial direction.

When using this method, since the middle position of the base ring 1 inthe axial direction is positioned at the intermediate portion 153 (themiddle position of the molding face in the axial direction) where theinternal diameter of the molding face of the metal mold 156 is thesmallest, more uniform molding can be performed.

FIGS. 25(a) to 25(d) illustrate a method for manufacturing a base ring.A base ring 171 shown in FIG. 25(a) is different from theabove-described base ring 1 in terms of a connecting portion (weld bead)172 oblique to the axial direction by butt welding. Due to the obliqueconnecting portion 172, weight balance of the base ring 171 in thecircumferential direction is improved compared with the base ring 1having the connecting portion 2 parallel to the axial direction.

A base ring 173 shown in FIG. 25(b) is formed by spirally curling arolled plate and connecting the joints, and has a connecting portion(weld bead) 174 making a circuit of the cylinder. Although theconnecting portion of the base ring 173 is long, weight balance of thebase ring 173 in the circumferential direction is excellent.

FIG. 25(c) illustrates a method for manufacturing a plurality of baserings 173 by producing a spiral tube in advance by spirally curling arolled plate and connecting the joints, and by cutting the tube to apredetermined length (cutting positions are indicated by virtual lines).

FIG. 25(d) illustrates a method for manufacturing a plurality of baserings 175 by producing a spiral tube having a dense connecting portion176, and by cutting the tube to a predetermined length (cuttingpositions are indicated by virtual lines). Although the connectingportions 176 of these base rings 175 are made longer, weight balance ofthe base rings 175 in the circumferential direction is excellent.

EXAMPLE

A base ring similar to that shown in FIG. 1 was molded from a plate ofan aluminum alloy, and a cylindrical ring with beads was produced bymolding the base ring by electromagnetic forming.

The aluminum-alloy plate as a raw material was an extruded plate (type6061-F). The plate was formed into a cylinder by roll-bending usingthree rolls such that the extruding direction corresponded to thefeeding direction of the roll-bending, and the ends were butt-welded(the connecting portion was parallel to the central axis direction ofthe ring). The cylindrical ring had a thickness of 2.2 mm, an internaldiameter of 494 mm, and a width of 222 mm in the axial direction. Forwelding, laser welding and MIG welding were performed. The laser weldingwas performed under a condition with a power of 40 kW, a speed of 3m/min, a wire A5356WY with a diameter of 1.2 mm, a feeding speed of 4m/min, and an atmospheric gas of 100% argon supplied at 25 l/min. TheMIG welding was performed under a condition with a current of 80 A, avoltage of 18 V, a wire A5356WY with a diameter of 1.2 mm, a feedingspeed of 60 cm/min, and an atmospheric gas of 100% argon supplied at 15l/min.

Then, this base ring was molded by electromagnetic forming (flaring)using a metal mold and a coil component for electromagnetic formingsimilar to those shown in FIG. 4. The minimum diameter of the moldingface of the metal mold (the diameter between parallel portions at bothends) was 504 mm, the diameter of the coil component was 490 mm, and thelength of the stabilized magnetic-field area of the coil component (thearea where substantially the same magnetic flux density is obtained) was250 mm. The cylindrical ring was disposed in the center of thisstabilized magnetic-field area, and the applied energy was 45 kJ.

FIG. 2 illustrates a cylindrical ring with beads molded byelectromagnetic forming. In both welding methods, the cylindrical ringhad an internal diameter of 500 mm, an external diameter of 570 mm, athickness of 2 mm at the ends, and a width of 192 mm in the axialdirection; and was molded into a shape along the molding face of themetal mold without any dents on the beads.

INDUSTRIAL APPLICABILITY

According to the present invention, an accurate cylindrical ring withbeads can be produced by electromagnetic forming at low cost and withhigh productivity. Furthermore, the cylindrical ring molded by flaringhas excellent properties as a reinforced ring especially for a flattire.

1. A method for manufacturing a cylindrical ring with beads, comprisingthe steps of: disposing a metal mold adjacent to the outer circumferenceor the inner circumference of a closed metallic base ring, the metalmold having a molding face that faces the base ring and having groovesfor forming the beads on the molding face along the circumferentialdirection; disposing a coil for electromagnetic forming at the oppositeside of the metal mold such that the base ring is interposedtherebetween; applying a momentary large current to the coil in thisarrangement; and deforming the base ring by pressing the base ringtoward the molding face of the metal mold such that the base ring ismolded into a shape corresponding to the molding face by electromagneticforming, wherein the molding face of the metal mold is substantiallysymmetrical with respect to a plane vertical to the axial direction atthe central position of the axial direction.
 2. The method formanufacturing the cylindrical ring with the beads according to claim 1,wherein the central position of the base ring in the axial directioncorresponds to that of the metal mold in the axial direction.
 3. Amethod for manufacturing a cylindrical ring with beads, comprising thesteps of: disposing a metal mold adjacent to the outer circumference orthe inner circumference of a closed metallic base ring, the metal moldhaving a molding face that faces the base ring and having grooves forforming the beads on the molding face along the circumferentialdirection; disposing a coil for electromagnetic forming at the oppositeside of the metal mold such that the base ring is interposedtherebetween; applying a momentary large current to the coil in thisarrangement; and deforming the base ring by pressing the base ringtoward the molding face of the metal mold such that the base ring ismolded into a shape corresponding to the molding face by electromagneticforming, wherein the grooves on the metal mold have holes communicatingwith the exterior of the grooves.
 4. A method for manufacturing acylindrical ring with beads, comprising the steps of: disposing a metalmold adjacent to the outer circumference or the inner circumference of aclosed metallic base ring, the metal mold having a molding face thatfaces the base ring and having grooves for forming the beads on themolding face along the circumferential direction; disposing a coil forelectromagnetic forming at the opposite side of the metal mold such thatthe base ring is interposed therebetween; applying a momentary largecurrent to the coil in this arrangement; and deforming the base ring bypressing the base ring toward the molding face of the metal mold suchthat the base ring is molded into a shape corresponding to the moldingface by electromagnetic forming, wherein the metal mold comprises aplurality of pieces separable in the circumferential direction.
 5. Amethod for manufacturing a cylindrical ring with beads, comprising thesteps of: disposing a metal mold adjacent to the outer circumference orthe inner circumference of a closed metallic base ring, the metal moldhaving a molding face that faces the base ring and having grooves forforming the beads on the molding face along the circumferentialdirection; disposing a coil for electromagnetic forming at the oppositeside of the metal mold such that the base ring is interposedtherebetween; applying a momentary large current to the coil in thisarrangement; and deforming the base ring by pressing the base ringtoward the molding face of the metal mold such that the base ring ismolded into a shape corresponding to the molding face by electromagneticforming, wherein the metal mold comprises a plurality of mold segmentsseparable in the axial direction at the grooves; and a gap is providedbetween two adjacent mold segments in the axial direction.
 6. A methodfor manufacturing a cylindrical ring with beads, comprising the stepsof: disposing a metal mold adjacent to the outer circumference or theinner circumference of a closed metallic base ring, the metal moldhaving a molding face that faces the base ring and having grooves forforming the beads on the molding face along the circumferentialdirection; disposing a coil for electromagnetic forming at the oppositeside of the metal mold such that the base ring is interposedtherebetween; applying a momentary large current to the coil in thisarrangement; and deforming the base ring by pressing the base ringtoward the molding face of the metal mold such that the base ring ismolded into a shape corresponding to the molding face by electromagneticforming, wherein an inner roll and an outer roll of which outerdimensions are finished with a required accuracy are prepared; and thecylindrical ring with the beads molded into the shape corresponding tothe molding face by electromagnetic forming is corrected by rotating therolls while interposing the cylindrical ring between the inner roll andthe outer roll.
 7. A method for manufacturing a cylindrical ring withbeads, comprising the steps of: disposing a metal mold adjacent to theouter circumference or the inner circumference of a closed metallic basering, the metal mold having a molding face that faces the base ring andhaving grooves for forming the beads on the molding face along thecircumferential direction; disposing a coil for electromagnetic formingat the opposite side of the metal mold such that the base ring isinterposed therebetween; applying a momentary large current to the coilin this arrangement; and deforming the base ring by pressing the basering toward the molding face of the metal mold such that the base ringis molded into a shape corresponding to the molding face byelectromagnetic forming, wherein the step of applying the momentarylarge current to the coil is repeated a plurality number of times.
 8. Amethod for manufacturing a cylindrical ring with beads, comprising thesteps of: disposing a metal mold adjacent to the outer circumference orthe inner circumference of a closed metallic base ring, the metal moldhaving a molding face that faces the base ring and having grooves forforming the beads on the molding face along the circumferentialdirection; disposing a coil for electromagnetic forming at the oppositeside of the metal mold such that the base ring is interposedtherebetween; applying a momentary large current to the coil in thisarrangement; and deforming the base ring by pressing the base ringtoward the molding face of the metal mold such that the base ring ismolded into a shape corresponding to the molding face by electromagneticforming, wherein the metal mold has a circular cutting blade vertical tothe axial direction; and the cutting blade cuts the base ring when thebase ring is pressed toward the molding face of the metal mold.
 9. Themethod for manufacturing the cylindrical ring with the beads accordingto claim 6, wherein at least one of the inner roll and the outer rollhas a cutting blade; and the cutting blade cuts the cylindrical ringwith the beads when the cylindrical ring with the beads is pressedtoward the roll having the cutting blade.
 10. A method for manufacturinga cylindrical ring with beads, comprising the steps of: disposing ametal mold adjacent to the outer circumference or the innercircumference of a closed metallic base ring, the metal mold having amolding face that faces the base ring and having grooves for forming thebeads on the molding face along the circumferential direction; disposinga coil for electromagnetic forming at the opposite side of the metalmold such that the base ring is interposed therebetween; applying amomentary large current to the coil in this arrangement; and deformingthe base ring by pressing the base ring toward the molding face of themetal mold such that the base ring is molded into a shape correspondingto the molding face by electromagnetic forming, wherein the base ringhas a large number of holes in the circumferential wall.
 11. The methodfor manufacturing the cylindrical ring with the beads according to claim10, wherein the large number of holes are formed in the base ring alongthe circumferential direction at positions where portions of the basering enter the interior of the grooves from the exterior of the groovesof the molding face of the metal mold in electromagnetic forming. 12.The method for manufacturing the cylindrical ring with the beadsaccording to claim 10, wherein the large number of holes are formed inthe base ring along the circumferential direction at both end portionsof the base ring in the axial direction.
 13. A method for manufacturinga cylindrical ring with beads, comprising the steps of: disposing ametal mold adjacent to the outer circumference or the innercircumference of a closed metallic base ring, the metal mold having amolding face that faces the base ring and having grooves for forming thebeads on the molding face along the circumferential direction; disposinga coil for electromagnetic forming at the opposite side of the metalmold such that the base ring is interposed therebetween; applying amomentary large current to the coil in this arrangement; and deformingthe base ring by pressing the base ring toward the molding face of themetal mold such that the base ring is molded into a shape correspondingto the molding face by electromagnetic forming, wherein a large numberof projections are formed in the molding face of the metal mold alongthe circumferential direction at positions nearest to the base ring; alarge number of holes are formed in the base ring along thecircumferential direction at positions corresponding to the projections;and the projections are fitted into the holes when the metal mold is putin position.
 14. The method for manufacturing the cylindrical ring withthe beads according to claim 13, wherein the projections are formedbetween two adjacent grooves on the molding face at the central positionof the molding face of the metal mold in the axial direction; and theholes are formed at the central position of the base ring in the axialdirection.
 15. A method for manufacturing a cylindrical ring with beads,comprising the steps of: disposing a metal mold adjacent to the outercircumference or the inner circumference of a closed metallic base ring,the metal mold having a molding face that faces the base ring and havinggrooves for forming the beads on the molding face along thecircumferential direction; disposing a coil for electromagnetic formingat the opposite side of the metal mold such that the base ring isinterposed therebetween; applying a momentary large current to the coilin this arrangement; and deforming the base ring by pressing the basering toward the molding face of the metal mold such that the base ringis molded into a shape corresponding to the molding face byelectromagnetic forming, wherein the base ring is in contact with themolding face of the metal mold at the central position of the moldingface of the metal mold in the axial direction.
 16. A metal mold formolding a cylindrical ring with beads by electromagnetic forming,comprising: a ring-shaped molding face on the inner surface or the outersurface; and grooves for forming the beads on the molding face along thecircumferential direction, wherein the metal mold has holes in thegrooves communicating with the exterior of the grooves.
 17. A metal moldfor molding a cylindrical ring with beads by electromagnetic forming,comprising: a ring-shaped molding face on the inner surface or the outersurface; and grooves for forming the beads on the molding face along thecircumferential direction, wherein the metal mold comprises a pluralityof pieces separable in the circumferential direction of the moldingface.
 18. A metal mold for molding a cylindrical ring with beads byelectromagnetic forming, comprising: a ring-shaped molding face on theinner surface or the outer surface; and grooves for forming the beads onthe molding face along the circumferential direction, wherein the metalmold comprises a plurality of mold segments separable in the axialdirection of the molding face at the grooves; and a gap is providedbetween two adjacent mold segments in the axial direction of the moldingface.
 19. A metal mold for molding a cylindrical ring with beads byelectromagnetic forming, comprising: a ring-shaped molding face on theinner surface or the outer surface; and grooves for forming the beads onthe molding face along the circumferential direction, wherein the metalmold has a circular cutting blade vertical to the axial direction of themolding face.
 20. A metal mold for molding a cylindrical ring with beadsby electromagnetic forming, comprising: a ring-shaped molding face onthe inner surface or the outer surface; and grooves for forming thebeads on the molding face along the circumferential direction, whereinthe metal mold further has a large number of positioning projections onthe molding face along the circumferential direction at positionsnearest to the base ring to be molded.
 21. A metal mold for molding acylindrical ring with beads by electromagnetic forming, comprising: aring-shaped molding face on the inner surface or the outer surface; andgrooves for forming the beads on the molding face along thecircumferential direction, wherein the metal mold protrudes to themaximum at the central position of the molding face in the axialdirection.